The ventral surface of the chick embryo of 18 hours incubation age presents a flourishing display of microvilli, blebs and ruffles, chiefly located at the margins of contiguous cells. The normal morphology of these structures will be studied externally by scanning electron microscopy and internally by transmission electron microscopy (including high voltage electron microscopy) with conventional and freeze-cleaving techniques. The effect of experimentally altered environments will be studied by immersion of the blastoderm from a few seconds to about five minutes in solutions of variable tonicity, pH, electrolyte concentrations and physiologically active solutions of colchicine, colecemid, cytochalasin B, etc.